1. Technical Field
The present invention relates to a light-emitting device module and an atomic oscillator.
2. Related Art
An atomic oscillator by an electromagnetically induced transparency (EIT) system (also referred to as coherent population trapping (CPT) system) is an oscillator that makes use of a phenomenon in which, when two kinds of resonance light having coherency and having specific wavelengths (frequencies) different from each other are simultaneously irradiated on an alkali metal atom, absorption of the resonance light stops (see U.S. Pat. No. 6,320,472).
The atomic oscillator can realize a highly accurate oscillator by accurately controlling a frequency difference between two kinds of light as explained above. As a light-emitting device that emits such two kinds of light, for example, a semiconductor laser is used.
A light-emitting device is desirably subjected to temperature control at high accuracy. For example, if the temperature of the light-emitting device deviates from a desired temperature, the frequency of light emitted from the light-emitting device fluctuates and frequency accuracy of the light-emitting device is deteriorated. In particular, when the light-emitting device is used as a light source for an atomic oscillator, as explained above, it is necessary to accurately control a frequency difference between two kinds of light. Therefore, even a small fluctuation in frequencies causes a problem.